Ion implantation is an important processing step in manufacturing semiconductor devices. In the ion implantation process, a beam of impurity ions is accelerated to kinetic energies ranging from several keV to several MeV and directed onto the surface of the semiconductor. A typical ion implanter ionizes the desired impurity gas in an arc chamber and the ions are extracted by an energized extraction electrode assembly into an acceleration tube toward the semiconductor.
The extraction electrode assembly typically includes two electrodes, a suppression electrode and an extraction electrode. As the ions are drawn out of the arc chamber or ion source, they pass through an aperture in the suppression electrode and toward an aperture in the extraction electrode. The majority of the ions pass through the extraction electrode aperture, but some strike the extraction electrode and generate secondary electrons. These secondary electrons are drawn by the highly positive source and accelerate toward it. The striking of the secondary electrons on the ion source would have resulted in the release of X-rays. However, these secondary electrons are stopped by the suppression electrode so that the generation of X-rays is greatly minimized.
In addition to extracting the ions from the arc chamber, the extraction electrode assembly further performs beam steering and focusing functions. The extraction electrode can be tilted and moved relative to the stationary ion source to center and focus the ion beam.
Because the suppression electrode is subjected to bombardment of high energy ions, the aperture is worn down quickly. A worn aperture may no longer have a well-defined opening and cannot steer and focus the ion beam in an effective manner. Because the suppression electrode is manufactured from a fragile material, typically graphite, careless mishandling also can easily damage the aperture and the electrode itself. Carelessness during the alignment process while installing the suppression electrode also may chip the aperture. When the aperture is damaged, the entire suppression electrode must be replaced, which is costly. Further, because of the porous and hydrophilic properties of graphite, substantial time is required to completely pump out the extraction chamber and out gas the suppression electrode after maintenance and servicing.